Add WithCallback Feature

[Not-Dhananjay-Mishra]

This PR implements the feature requested in [#3658] to allow configurable telemetry for the Client.

Modifications -

• WithCallback(callback func()) was added. The callback will be set by the user.
• The callback execute just before the client.bareDo inside client.Do.
• Allows for chaining because it returns the same Client instance.
• Added new Callback field in the Client struct of type func(), which default set to nil during initialize().

Example Code -

client := github.NewClient(nil).WithCallback(func() {
fmt.Println("Callback executed")
})

This enables users to attach custom telemetry or logging kind of things to API calls in a flexible, user friendly manner.
Btw this is my first PR
Happy to get any feedback or suggestions to improve it

[Not-Dhananjay-Mishra]

Corrected the typo that caused the lint issue. I’m still learning, so thank you

[gmlewis]

Thank you, @Not-Dhananjay-Mishra - but I don't think this fully satisfies what is being requested in #3658.

Additionally, discussion has not completed in that issue, as there is an outstanding request to the original author to further clarify their request, so it is premature to be writing any PR for that issue yet.

Let's hold off on this PR until we get some more clarity, please.

[Not-Dhananjay-Mishra]

Thanks @gmlewis for the clarification! I will hold off on the PR. I appreciate the guidance.